The present invention relates to a visual display, particularly though not exclusively for use with data processing apparatus.
Visual displays for data processing apparatus, such as computers, are normally field emission displays of the cathode ray tube type. These generally have a depth of the order of their size dimension, which conventionally is their corner to corner or diagonal dimension. This depth can render them inconvenient in use. Recently, laptop computers have become increasingly widely used. These incorporate a xe2x80x9cflatxe2x80x9d screen display, usually of the liquid crystal type.
Proposals have been made to provide displays having flat screen cathode ray tubes. These are known as Spindt cathodes, after the inventor of U.S. Pat. No. 3,755,704. In this specification, they are referred to as field emission devices.
The object of the present invention is to provide an improved method of sealing a xe2x80x9cflatxe2x80x9d screen field emission visual display and a machine therefor.
This application claims priority from our UK application No. 9720723.7 of Oct. 1, 1997 and Provisional Application No. 60/067,508 of Dec. 4, 1997. The priority applications describe both our field emission device invention and its manner of sealing into a display and a machine therefor. This specification describes both aspects and claims our sealing invention. A copending application filed on the same date herewith (PCT Ser. No. 08/766,474) similarly describes both aspects and claims the field emission device invention.
According to a first aspect of the invention there is provided a method of sealing a visual display having:
at least one field emission device including an emission layer on a substrate;
a glass face plate carrying excitable phosphor material; and
fused sealing material peripherally sealing the face plate to the emission device(s), whereby the face plate is parallelly spaced from the emission layer, the method consisting in the steps of:
evacuating the display, to evacuate the space between the emission layer and the face plate; and
irradiating a peripheral region of the face plate to fuse the sealing material, thereby sealingly securing the face plate to the emission device(s).
Preferably the face plate is positioned in pixel to pixel alignment with the emission device(s) subsequently to the start of the evacuation, preferably by robotic manipulation.
In accordance with a preferred feature of the invention, the irradiation is performed by traversing along the sealing material with an irradiation source, the traversing being by movement of the irradiation source or the face plate and emission device(s) or both.
In one embodiment, preliminarily to the traversing, irradiation is carried out at spaced intervals around the fusible sealing material to tack the face plate in position.
Normally, and in particular where the sealing material is fusible glass frit, the irradiation step is performed with a laser.
A plurality of lasers may be used for the irradiation step, either in sequence to assure complete flising of the frit and/or at opposite positions to allow speedy traverse.
Conveniently, at least a final part of the evacuation step is simultaneous with the irradiation step, particularly where frit is so shaped as to be able to bridge a face plate/carrier gap established by the height of spacers between the face plate and the emission layer of the emission device(s). Nevertheless, it can be envisaged that the evacuation and irradiation steps are carried out at sequential stations.
As an alternative wherein the sealing material is fusible under ultra-violet light, the irradiation step is performed by an ultra-violet light source, preferably with a mask restricting the irradiation to irradiate the adhesive only. In this alternative, a peripheral glass wall may be provided with UV curable adhesive at one surface in abutment with the face plate and at an opposite surface in contact with the carrier (see below) or the emission device and the irradiation fuses the adhesive at both surfaces. It can be envisaged that the carrier for the emission device may be of glass and permeable to UV light, whereby a spacer of the carrierxe2x80x94or indeed of the emission devicexe2x80x94from the face plate may have UV curing adhesive at both its top and bottom.
Normally the emission device(s) will be supported on a carrier and the method includes the step of preliminarily sealing the device(s) to the carrier.
Where the carrier supports a plurality of emission devices and the method may include the steps of:
positioning the emission devices in pixel line alignment and
provisionally securing the devices with respect to the carrier, prior to sealing, preferably by means of wedges between the emission devices and peripheral portions of the carrier.
The wedges can be of gettering material.
Alternatively, the emission devices and the carrier may be so complementarily spaced that they come into pixel line alignment on assembly into the carrier.
In the preferred embodiment, the emission device(s) are sealed to the carrier by soldering, the device(s) and the carrier being heated for melting of the solder and cooled for setting of it, the cooling preferably being provided on evacuation of a vacuum chamber with an outlet from the chamber directing air flow from the chamber to the solder joint for its cooling.
Whilst the carrier and emission device(s) can be heated to above the melting point of the solder in the vacuum chamber where the fusing of the sealing material is carried out, preferably they are heated to this temperature in a preceding vacuum chamber. Alternatively, it is possible for the soldering to be carried out in the ambient atmosphere.
The method preferably includes preliminary cleaning of the face plate and/or the emission device(s) by irradiating it or them with one or more electron beams and/or ion streams. This cleaning can be in the ambient atmosphere or under partial or complete vacuum.
Preferably the cleaning is carried out with a field effect emission device of the invention.
The method preferably includes including a step of irradiation of an activatable getter for final evacuation of the display. Particularly where the sealing irradiation is by laser, the getter irradiation is by a laser.
Apparatus for sealing a visual display having a field emission device with an emission layer on a substrate and a face plate with excitable phosphor material, the apparatus comprising:
a vacuum chamber, preferably including its own evacuation pump;
means in the vacuum chamber for supporting the field emission device and the face plate juxtaposed in pixel to pixel alignment; and
an irradiation device adapted and arranged to irradiate sealing material provided on the device or the face plate thereby fusing the material to seal the visual display.
Whilst it is envisaged that the irradiation device can be mounted inside the vacuum chamber; in the preferred embodiments, the irradiation device is mounted outside the vacuum chamber, the chamber being provided with a window through the irradiation can pass.
The preferred irradiation device is a laser; although it can be a ultraviolet light source.
Preferably, wherein the support means includes a manipulator for manoeuvring one of the field emission device and the face plate into pixel to pixel alignment with the other, and the apparatus includes means for measuring the relative position of the emission device and the face plate, whereby the manipulator can position them in pixel to pixel alignment.
Particularly where the irradiation device is a laser, the apparatus preferably includes heater(s) for heating the emission device and face plate prior to irradiation. Preferably, at least some of the heaters of the vacuum chamber are arranged outside the window provided for the irradiation to enter the chamber. Conveniently, these heaters are arranged on a frame so that they can be swung, preferably about hinges, clear of the window to expose it to the irradiation device
In one preferred embodiment, the apparatus includes a pre-heating and preliminary evacuation chamber provided with heater(s), an evacuation pump and means for transferring the emission device and face plate to the vacuum chamber.
Preferably, the apparatus also includes a cooling chamber provided with means for controlling the cooling of the visual display and means for transferring the visual display from the vacuum chamber. Normally, the transfer means are adapted to transfer the emission device(s) as assembled onto a carrier.
Preferably, the heaters of the preliminary evacuation chamber are adapted to heat the emission device(s) and the carrier to sufficient temperature to melt solder and the evacuation means is adapted to direct evacuated air flow to the solder region to cool it after melting.
Further the apparatus preferably includes means for manoeuvring the emission device(s) with respect to the carrier for their soldering in desired relative position.
In one preferred embodiment, the sealing apparatus includes a robotic input station and removable input pods adapted to be connected thereto, the removable input pods being adapted to accommodate a plurality of emission devices and face plates, preferably in cassettes themselves removably mounted in the input pods. The robotic input station is adapted to unload the emission devices and the face plates from the input pods for processing in the apparatus. The removable input pods conveniently include means for their heating and/or evacuation.
Preferably, a robotic output station with a removable output pod is also provided. The robotic output station is adapted to remove sealed displays from the vacuum chamber and load them into an output pod, the latter having means for controllably returning the sealed displays to ambient pressure and temperature.